A vital characteristic of living systems is their ability to perform efficient energy conversion. Biological energy transduction is the ensemble of pathways necessary for cellular energy (ATP) production, which is essential for many cellular functions, including macromolecular biosynthesis, solute transport, signal transduction, chemotaxis, phototaxis and thermogenesis. The long term goal of this project is to define the cytochrome (cyt) components of these pathways, and to understand their structure, mechanism of function and biogenesis (i.e., assembly, maturation and regulation). Facultative phototrophic bacteria (e.g., Rhodobacter species) provide an excellent model system for eukaryotic organelles. The energy transduction complexes are widespread among living organisms, and their improper function leads to devastating neuromuscular and mitochondrial diseases in humans, and low crop yields in plants. This project will continue molecular and biochemical genetics of these complexes, focusing on the structure, function and biogenesis of membrane-bound, multisubunit cyt c complexes (i.e., the ubihydroquinone: cyt c oxidoreductase, or the bc1 complex, and the cbb3-type cyt c oxidase). Major progress has recently been accomplished by the resolution of the 3D structure of the bc1 complex, and recognition of the mobility of its FeS protein subunit. in the light of these excitements, the specific aims include the analysis of the FeS protein motion and its control during Q0 site catalysis; direct and rapid activation of the bc1 complex using photoactivatable compounds to study the movement of the FeS protein as a unique intra-protein electron shuttle device; construction of novel cyt c1 molecules with unusual ligand and folding properties; engineering of novel bc1 complex variants to correlate their structural flexibility and functional similarities; and genetic and biochemical studies of mutants and gene products involved in the biogenesis of multisubunit cyt c complexes and incorporation of their prosthetic group. These studies will increase significantly our understanding of the structure and mechanism of function of the bc1 complex as a prototype for a unique intra-protein electron shuttle device, and pave the road to future "single molecule" studies. They will also provide important insights into the biogenesis of membrane-bound multisubunit cyt c complexes that operate during cellular energy production, an important biological process that is far from being completely understood, even in bacteria. Finally, insights gained in this simpler system are generally applicable to the structurally more complex and yet functionally similar organelle-derived complexes, and are important for the elucidation of the molecular basis of mitochondrial diseases and aging.